The relationship between pressure and flow in the portal system will be assessed in subjects with normal splanchnic and and hepatic vascular beds and in patients with cirrhosis of the liver with and without portasystemic shunting. Total hepatic blood flow will be measured either by an indicator dilution technique using hepatic arterial injection of I-131 albumin, or by measuring the clearance of indocyanine green dye across the liver. Portasystemic shunting will be assessed by calculating the fraction of I-131 albumin shunted in prehepatic portasystemic communications after injection into the splenic artery an superior mesenteric artery. The portal pressure will be assessed as the wedge hepatic venous pressure. Portal inflow will be reduced acutely by systemic or local administration of pitressin or other vasoconstrictor drugs, exercise and transient occlusion of the splenic artery with a balloon tipped catheter. Increases in portal flow will be induced by a glucagon infusion, by ingestion of food and by vasodilator drug infusion. Changes in total hepatic blood flow and in the fraction of portal flow bypassing the liver through portasystemic shunts will be assessed. The relationship between changes in flow and changes in pressure will be evaluated during these varied physiologic and pharmacologic interventions. Circulating glucagon levels will be measured during both glucagon infusion and during endogenously induced hyperglucagonemia to determine if glucagon secretion with resultant high portal inflow could be a factor in acute rises in portal pressure or acute increases in portasystemic shunting.